One of the most famous verses in the Bible is probably 1 John 4:8, which says that “God is love.” This phrase has often been understood to have Trinitarian implications. If God is love in His essence, then there must be persons in God who share love with one another. It would not be an exaggeration to say that 1 John 4:8 is an incredibly important Bible verse.
On another subject, it would also probably not be an exaggeration to say that John Calvin is one of the most influential voices in the history of Christianity. True, what we today call the Protestant Reformation began with professor Martin Luther; however, it was certainly Calvin who gave Protestantism is characteristic vigor. It was Calvin’s Institutes of the Christian Religion that changed the Protestant Reformation from a marginal sect of Christendom to an intellectual tradition in its own right.
One of the most recognizable aspects of John Calvin’s theology is his belief not only in the predestination of the elect for salvation in Christ and eternal life, but also in the predestination of the non-elect (the “reprobate”) for damnation apart from Christ and eternal punishment. The title of chapter twenty-one in book three of Calvin’s institutes reads thus: “Of the eternal election, by which God has predestinated some to salvation, and others to destruction.”
Throughout the history of Reformed (Calvinist) thought, several figures have diverged from Calvin’s understanding of predestination and election, notably Jacobus Arminius (the father of “Arminian” theology, which ironically was originally a tradition within Calvinism proper) and Karl Barth. But the ominous picture of God that Calvin painted remains all too present in the minds of both Christians and non-Christians alike.
In light of Calvin’s understanding of election and predestination, how did he understand 1 John 4:8? If we take 1 John 4:8 at face value (admittedly not the best thing to do when reading literature that is four times older than Shakespeare), it would seem to teach that God is love in His very essence and that nothing He can do can be incompatible with love. If this is the case, it is difficult to imagine God predestinating anyone to destruction. This should especially be the case if God has the type of power that Calvinism claims that He does. Calvinists believe that God could elect everyone for salvation if He so pleased. Karl Barth, who was in many respects a Calvinist himself, took this rhetoric to its logical conclusion: universal salvation. All are elect; none are reprobate. Therefore, all will be saved.
Whatever certain of Calvin’s intellectual heirs might have said about election and predestination, Calvin himself was clear: there are those who are predestined for eternal misery. It would seem that Calvin did not believe that God was love in His essence, for surely a loving God with the power to override a human’s ability to reject the good would use that power on everyone. Alas, for Calvin it is not so. Here is Calvin’s own treatment of the phrase “God is love.”
“Here then he does not speak of the essence of God, but only shews what he is found to be by us.” 
That is, God is not love in His essence, but is merely experienced as love by those who are elected for salvation.
What does this mean for Trinitarian theology? If God is not love in His essence, do the Trinitarian persons love one another? Is God simple, or is Tritheism the logical conclusion of three gods selfishly competing for power, since power is really the only thing that actually matters in Calvin’s theology? The implications are almost boundless.
The take-away of all this, in my opinion, is to be wary of trusting only a single person for one’s theology. Surely they can only be called “Christian” who listen to the testimony of the entire church, and not simply the opinions of a few rag-tag men.
 Calvin’s commentary on 1 John 4: <http://biblehub.com/commentaries/calvin/1_john/4.htm>